This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To study SIV specific CD8+ T cell function, localization, and association with SIV infected cells in vivo in vaccinated and non-vaccinated macaques in order to gain insights into SIV pathogenesis. The Haase and Skinner lab groups worked together to determine the in vivo effector to target cell ratios of virus-specific CD8 T cells to virus-infected cells in lymphoid and genital tissues of SIV-infected rhesus macaques. They did this using a methodology developed in earlier years from this grant support termed in situ tetramer staining combined with in situ hybridization (ISTH) and found a significant correlation with reduction in virus-producing cells in lymphoid tissues and high effector to target ratios. They also began to investigate the phenotype of virus-specific CD8 T cells in situ by co-labeling tissues with tetramer reagents that stain virus-specific T cells and perforin and granulin antibodies. They also were successful in developing methods to triple labeling sections with tetramer reagents and two phenotypic antibodies. Analysis of these stained sections is ongoing. In addition, during the course of these studies they discovered previously undescribed populations of virus-specific T cells that appear to down modulate CD8 molecules in B cell follicles and in vaginal and cervical epithelium. This work used Immunology &Virology Services. Publications are pending.